1. Field of the Invention
This invention relates to a magnetic bubble device, and more particularly to a laminated magnetic bubble device of a multiple layer structure composed of at least two thin magnetic films such as, for example, a thin magnetic film having vertically oriented anisotropy and low coercive force which allows easy generation and erasure of magnetic bubbles and a thin magnetic film having vertically oriented anisotropy and high coercive force which is not affected by a magnetic field of low level used for generating the magnetic bubbles in the magnetic film of low coercive force. The bubble device can be adapted to a magnetic bubble memory or a magneto-optical element.
2. Description of the Prior Art
A conventional magnetic bubble element is, in general, constructed by laminating a magnetic thin film having vertically oriented anisotropy and low coercive force of less than 1 Oe on a substrate of GGG (gadolinium-gallium-garnet) or the like, for example, and then forming thereon a pattern of permalloy, ion-implanted garnet film or the like. As well known in the art, since a magnetic bubble can be easily propagated within such a pattern, it can be used as a magnetic bubble memory. The details of the magnetic bubble element are described in a literature by the inventor, of this invention, et al, entitled "MAGNETIC BUBBLE ELEMENTS" and presented on the Denki Gakkai Shi, Vol. 100, No. 3, Pages 215-218.
For a pattern for propagating a magnetic bubble, high information density as well as high operation speed are important requisites. At present, a major-minor system such a contiguous disc type as shown in FIG. 1, for example, is widely utilized. Since the ion-implanted garnet has such disadvantages that the direction of pattern formation is limited becase of crystal anisotropy due to ion implantation and others, it is most preferable to form a high density of contiguous disc by use of a permalloy. However, in the case of the permalloy parttern, if the density of a disc 2 within a minor loop 1 becomes high, there arises such a tendency that a bubble 3 moving within the disc jumps to an adjacent disc, or the bubble is erroneously propagated within the same disc from one side to the other side thereof, resulting in miss-information. These phenomena may result in an error of information. In FIG. 1, reference numeral 4 shows a major loop, 5 shows a transfer line and 6 shows a write-in line.